SWAMPSCOTT – Swampscott High School students headed back to school after an evacuation Monday morning.At a little before noon Monday Swampscott Police and Fire, emergency personnel and State Police bomb squad were sent to the high school for a report of a suspicious package.The package was a backpack that was left in the middle of a hallway. After the bomb squad inspected the backpack it was determined that only a battery was inside.”It was not a threat,” said Superintendent Lynne Celli. “The children were safe at all times.”The students and staff were evacuated to Upper Jackson Park during the ordeal.”The students are back in school for lunch and then will be debriefed,” Celli said.